Conjugate Pair of Foci

The position of the image from the third lens is (Assume each lens is thin lens)

What called conjugate?

WHY IS lens formula called conjugate foci relation?

What is conjugate foci of mirror?

What is conjugate focus of a lens?

What is Newton lens formula derived?

What is the formula of lens formula?

What is formula of conjugate foci method?

What do you mean by lens formula?

Two thin lenses of focal lengths $f_1$ and $f_2$ are placed in contact with each other. The focal length of the combination is

A convex lens $A$ of focal length 20 cm and a concave lens $B$ of focal length 56 cm are kept along the same axis with the distance $d$ between them. If a parallel beam of light falling on $A$ leaves $B$ as a parallel beam, then distances $d$ in cm will be